The invention pertains to a therapy system to deposit energy into a target zone.
Such a therapy system is known from the paper ‘Determination of the optimal delay between sonications during focused ultrasound surgery in rabbits by using MR imaging to monitor thermal build-up in vivo’ by N. J. McDannold et al. in Radiology 211 (1999) 419-426.
In this document an in vivo sonication experiment is mentioned in which a system for monitoring ablation of tissue is investigated. This known system monitors the ablation process in that heat damage to tissue in monitored. The known system for monitoring ablation performs monitoring e.g. on the basis of magnetic resonance images. Moreover, the cited document mentions that energy can be delivered as sonications in the form of focused ultrasound waves. Further it is mentioned that closely spaced sonications are delivered that are spaced by an intersonication delay to minimize thermal build-up. That is successive deposits of energy are separated in time by a cool-down period. To minimize this intersonication delay the temperature build-up should be measured during treatment. This temperature information is then used to control the intersonication delay.
The cool down period between successive deposits of energy allows temperature to reduce in a region around the focal region into which the energy is directly deposited. Thus, temperature build-up in the region around the focal region, i.e. the so-called off-focus temperature build-up, is reduced. Thus, the risk is reduced for thermal damage to healthy tissue outside of the focal region.
The known therapy system is provided with a thermometry module in the form of am MR imager to measure the temperature in a measurement field. Generally, the measurement field contains the focal region into which the energy is directly deposited. The duration of the cool down period between the successive deposits of energy is controlled on the basis of the measured temperature. In this way it is avoided that the time required for the successive deposits of energy is longer than necessary, while off-focus temperature build-up is avoided.